Four-piece infrared single wavelength lens system

ABSTRACT

A four-piece infrared single wavelength lens system includes, in order from the object side to the image side: a first lens element with a positive refractive power having an object-side surface being convex near an optical axis and an image-side surface being concave near the optical axis, a stop, a second lens element with a refractive power, a third lens element with a positive refractive power having an object-side surface being concave near the optical axis and an image-side surface being convex near the optical axis, a fourth lens element with a negative refractive power having an object-side surface being convex near the optical axis and an image-side surface being concave near the optical axis. Such arrangements can provide a four-piece infrared single wavelength lens system which has a wide field of view, high resolution, short length and less distortion.

BACKGROUND Field of the Invention

The present invention relates to a lens system, and more particularly toa miniaturized four-piece infrared single wavelength lens systemapplicable to electronic products.

Description of the Prior Art

Nowadays digital imaging technology is constantly innovating andchanging, in particular, digital carriers, such as, digital camera andmobile phone and so on, have become smaller in size, so CCD (ChargeCoupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensoris also required to be more compact. In addition to be used in the fieldof photography, in recent years, infrared focusing lens has also be usedin infrared receiving and sensing field of the game machine, and inorder to make the scope of game machine induction user more broader,wide-angle lens group has become the mainstream for receiving infraredwavelength at present.

The applicant has also put forward a number of lens groups related toinfrared wavelength reception, however, at present, the game machine isbased on a more three-dimensional, real and immediate 3D game, thecurrent or the applicant's previous lens groups are all 2D plane games,which cannot meet the 3D game focusing on the deep induction efficacy.

Special infrared receiving and induction lens groups for game machinesare made of plastic for the pursuit of low cost, however, poor materialtransparency is one of the key factors that affect the depth detectionaccuracy of the game machine, and plastic lenses are easy to overheat ortoo cold in ambient temperature, so that the focal length of the lensgroup will be changed and cannot focus accurately. Therefore, thecurrent infrared receiving and induction lens groups cannot meet the 3Dgame depth precise induction requirement.

The present invention mitigates and/or obviates the aforementioneddisadvantages.

SUMMARY

The primary objective of the present invention is to provide afour-piece infrared single wavelength lens system which has a wide fieldof view, high resolution, short length and less distortion.

Therefore, a four-piece infrared single wavelength lens system inaccordance with the present invention comprises, in order from an objectside to an image side: a first lens element with a positive refractivepower having an object-side surface being convex near an optical axisand an image-side surface being concave near the optical axis, at leastone of the object-side surface and the image-side surface of the firstlens element being aspheric; a stop; a second lens element with arefractive power, at least one of an object-side surface and animage-side surface of the second lens element being aspheric; a thirdlens element with a positive refractive power having an object-sidesurface being concave near the optical axis and an image-side surfacebeing convex near the optical axis, at least one of the object-sidesurface and the image-side surface of the third lens element beingaspheric; and a fourth lens element with a negative refractive powerhaving an object-side surface being convex near the optical axis and animage-side surface being concave near the optical axis, at least one ofthe object-side surface and the image-side surface of the fourth lenselement being aspheric.

Preferably, a focal length of the first lens element is f1, a focallength of the second lens element is f2, and they satisfy the relation:−1.0<f1/f2<1.0, so that the refractive power of the first lens elementand the second lens element are more suitable, it will be favorable toobtain a wide field of view and avoid the excessive increase ofaberration of the system.

Preferably, the focal length of the second lens element is f2, a focallength of the third lens element is f3, and they satisfy the relation:−10.4<f2/f3<13.8, which can improve the peripheral resolution andilluminance of the system.

Preferably, the focal length of the third lens element is f3, a focallength of the fourth lens element is f4, and they satisfy the relation:−1.0<f3/f4<−0.1, so that the refractive power of the system can bebalanced effectively, it will be favorable to reduce the sensitivity ofthe system, improving the yield of production.

Preferably, the focal length of the first lens element is f1, the focallength of the third lens element is f3, and they satisfy the relation:1.4<f1/f3<3.0, so that the positive refractive power of the first lenselement can be distributed effectively, so as to reduce the sensitivityof the four-piece infrared single wavelength lens system.

Preferably, the focal length of the first lens element is f1, the focallength of the fourth lens element is f4, and they satisfy the relation:−2.1<f1/f4<−0.5, so that the positive refractive power of the first lenselement can be distributed effectively, so as to reduce the sensitivityof the four-piece infrared single wavelength lens system.

Preferably, the focal length of the second lens element is f2, the focallength of the fourth lens element is f4, and they satisfy the relation:−9.0<f2/f4<7.1, so that the distribution of the positive refractivepower will be appropriate, it will be favorable to correct theaberration of the system and improve the image quality.

Preferably, the focal length of the first lens element is f1, a focallength of the second lens element and the third lens element combined isf23, and they satisfy the relation: 1.2<f1/f23<3.1. If f1/f23 satisfiesthe above relation, a wide field of view can be obtained and theresolution can be improved evidently.

Preferably, a focal length of the first lens element and the second lenselement combined is f12, a focal length of the third lens element andthe fourth lens element combined is f34, and they satisfy the relation:0.48<f12/f34<2.23, which is favorable to obtain a wide field of view,and effectively correct image distortion.

Preferably, the focal length of the second lens element is f2, the focallength of the third lens element and the fourth lens element combined isf34, and they satisfy the relation: −5.3<f2/f34<6.7, which is favorableto obtain a wide field of view, and effectively correct imagedistortion.

Preferably, the focal length of the second lens element and the thirdlens element combined is f23, the focal length of the fourth lenselement is f4, and they satisfy the relation: −1.0<f23/f4<−0.2, which isfavorable to obtain a wide field of view, and effectively correct imagedistortion.

Preferably, the focal length of the first lens element is f1, a focallength of the second lens element, the third lens element and the fourthlens element combined is f234, and they satisfy the relation:0.7<f1/f234<1.8, which is favorable to obtain a wide field of view, andeffectively correct image distortion.

Preferably, a focal length of the first lens element, the second lenselement and the third lens element combined is f123, the focal length ofthe fourth lens element is f4, and they satisfy the relation:−1.0<f123/f4<−0.15, which is favorable to obtain a wide field of view,and effectively correct image distortion.

Preferably, a refractive index of the fourth lens element is N4, an Abbenumber of the fourth lens element is V4, and they satisfy the relations:1.61<N4; V4<25, it will be favorable to permeate the four-piece infraredsingle wavelength lens system, so as to reduce the absorptivity ofinfrared single wavelength in the lens system.

Preferably, a focal length of the four-piece infrared single wavelengthlens system is f, a distance from the object-side surface of the firstlens element to the image plane along the optical axis is TL, and theysatisfy the relation: 0.4<f/TL<0.85, it will be favorable to maintainthe objective of miniaturization and long focus of the four-pieceinfrared single wavelength lens system, which can be used in thinelectronic products.

The present invention will be presented in further details from thefollowing descriptions with the accompanying drawings, which show, forpurpose of illustrations only, the preferred embodiments in accordancewith the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a four-piece infrared single wavelength lens system inaccordance with a first embodiment of the present invention;

FIG. 1B shows the image plane curve and the distortion curve of thefirst embodiment of the present invention;

FIG. 2A shows a four-piece infrared single wavelength lens system inaccordance with a second embodiment of the present invention;

FIG. 2B shows the image plane curve and the distortion curve of thesecond embodiment of the present invention;

FIG. 3A shows a four-piece infrared single wavelength lens system inaccordance with a third embodiment of the present invention;

FIG. 3B shows the image plane curve and the distortion curve of thethird embodiment of the present invention;

FIG. 4A shows a four-piece infrared single wavelength lens system inaccordance with a fourth embodiment of the present invention;

FIG. 4B shows the image plane curve and the distortion curve of thefourth embodiment of the present invention;

FIG. 5A shows a four-piece infrared single wavelength lens system inaccordance with a fifth embodiment of the present invention; and

FIG. 5B shows the image plane curve and the distortion curve of thefifth embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1A and 1B, FIG. 1A shows a four-piece infrared singlewavelength lens system in accordance with a first embodiment of thepresent invention, and FIG. 1B shows, in order from left to right, theimage plane curve and the distortion curve of the first embodiment ofthe present invention. A four-piece infrared single wavelength lenssystem in accordance with the first embodiment of the present inventioncomprises a stop 100 and a lens group. The lens group comprises, inorder from an object side to an image side: a first lens element 110, asecond lens element 120, a third lens element 130, a fourth lens element140, an IR cut filter 170, and an image plane 180, wherein thefour-piece infrared single wavelength lens system has a total of fourlens elements with refractive power. The stop 100 is disposed between animage-side surface 112 of the first lens element 110 and an object-sidesurface 121 of the second lens element 120.

The first lens element 110 with a positive refractive power has anobject-side surface 111 being convex near an optical axis 190 and theimage-side surface 112 being concave near the optical axis 190, theobject-side surface 111 and the image-side surface 112 are aspheric, andthe first lens element 110 is made of plastic material.

The second lens element 120 with a positive refractive power has theobject-side surface 121 being concave near the optical axis 190 and animage-side surface 122 being convex near the optical axis 190, theobject-side surface 121 and the image-side surface 122 are aspheric, andthe second lens element 120 is made of plastic material.

The third lens element 130 with a positive refractive power has anobject-side surface 131 being concave near the optical axis 190 and animage-side surface 132 being convex near the optical axis 190, theobject-side surface 131 and the image-side surface 132 are aspheric, andthe third lens element 130 is made of plastic material.

The fourth lens element 140 with a negative refractive power has anobject-side surface 141 being convex near the optical axis 190 and animage-side surface 142 being concave near the optical axis 190, theobject-side surface 141 and the image-side surface 142 are aspheric, thefourth lens element 140 is made of plastic material, and at least one ofthe object-side surface 141 and the image-side surface 142 is providedwith at least one inflection point.

The IR cut filter 170 made of glass is located between the fourth lenselement 140 and the image plane 180 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The equation for the aspheric surface profiles of the respective lenselements of the first embodiment is expressed as follows:

$z = {\frac{{ch}^{2}}{1 + \left\lbrack {1 - {\left( {k + 1} \right)c^{2}h^{2}}} \right\rbrack^{0.5}} + {A\; h^{4}} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Gh}^{14} + \ldots}$

wherein:

z represents the value of a reference position with respect to a vertexof the surface of a lens and a position with a height h along theoptical axis 190;

c represents a paraxial curvature equal to 1/R (R: a paraxial radius ofcurvature);

h represents a vertical distance from the point on the curve of theaspheric surface to the optical axis 190;

k represents the conic constant;

A

B

C

D

E

G

. . . : represent the high-order aspheric coefficients.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a focal length of the four-piece infrared singlewavelength lens system is f, a f-number of the four-piece infraredsingle wavelength lens system is Fno, the four-piece infrared singlewavelength lens system has a maximum view angle (field of view) FOV, andthey satisfy the relations: f=2.52 mm; Fno=1.94; and FOV=91.4 degrees.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a focal length of the first lens element 110 isf1, a focal length of the second lens element 120 is f2, and theysatisfy the relation: f1/f2=0.31.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the second lens element 120is f2, a focal length of the third lens element 130 is f3, and theysatisfy the relation: f2/f3=7.88.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the third lens element 130is f3, a focal length of the fourth lens element 140 is f4, and theysatisfy the relation: f3/f4=−0.69.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, the focal length of the third lens element 130 is f3, and theysatisfy the relation: f1/f3=2.47.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, the focal length of the fourth lens element 140 is f4, and theysatisfy the relation: f1/f4=−1.69.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the second lens element 120is 12, the focal length of the fourth lens element 140 is f4, and theysatisfy the relation: f2/f4=−5.40.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, a focal length of the second lens element 120 and the third lenselement 130 combined is f23, and they satisfy the relation: f1/f23=2.68.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a focal length of the first lens element 110 andthe second lens element 120 combined is f12, a focal length of the thirdlens element 130 and the fourth lens element 140 combined is f34, andthey satisfy the relation: f12/f34=0.89.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the second lens element 120is f2, the focal length of the third lens element 130 and the fourthlens element 140 combined is f34, and they satisfy the relation:f2/f34=3.45.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the second lens element 120and the third lens element 130 combined is f23, the focal length of thefourth lens element 140 is f4, and they satisfy the relation:f23/f4=−0.63.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, a focal length of the second lens element 120, the third lenselement 130 and the fourth lens element 140 combined is f234, and theysatisfy the relation: f1/f234=1.39.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a focal length of the first lens element 110,the second lens element 120 and the third lens element 130 combined isf123, the focal length of the fourth lens element 140 is f4, and theysatisfy the relation: f123/f4=−0.66.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the four-piece infraredsingle wavelength lens system is f, a distance from the object-sidesurface 111 of the first lens element 110 to the image plane 180 alongthe optical axis 190 is TL, and they satisfy the relation: f/TL=0.61.

The detailed optical data of the first embodiment is shown in table 1,and the aspheric surface data is shown in table 2.

TABLE 1 Embodiment 1 f(focal length) = 2.52 mm, Fno = 1.94, FOV = 91.4deg. Focal surface Curvature Radius Thickness Material Index Abbe #length 0 object infinity 350 1 infinity 0 2 Lens 1 1.769 (ASP) 0.381plastic 1.636 24 4.91 3 3.934 (ASP) 0.081 4 stop infinity 0.416 0.418 5Lens 2 −9.761 (ASP) 0.445 plastic 1.636 24 15.68 6 −4.927 (ASP) 0.266 7Lens 3 −1.513 (ASP) 0.732 plastic 1.636 24 1.99 8 −0.799 (ASP) 0.032 9Lens 4 1.521 (ASP) 0.455 plastic 1.636 24 −2.90 10 0.727 (ASP) 0.638 11IR-filter infinity 0.300 glass 1.517 64.2 12 infinity 0.400 13 Imageinfinity infinity plane

TABLE 2 Aspheric Coefficients surface 2 3 5 6 K: −1.9854E+00 −5.8734E+01−1.8733E+02 −2.3060E+00 A:   5.1703E−02   1.1583E−01 −2.3906E−01−1.6839E−01 B:   2.9749E−02 −4.0107E−01 −1.6786E−01   7.6889E−02 C:−2.6234E−01   1.2453E+00   1.5452E−01 −4.8132E−01 D:   8.3016E−01−3.0280E+00 −1.8671E+00   7.6365E−01 E: −1.3260E+00   2.4666E+00  3.3053E+00 −6.9186E−01 F:   6.7208E−01   1.0341E−01 −3.6288E+00  2.5833E−01 surface 7 8 9 10 K:   3.7357E−01 −1.0406E+00 −1.3743E+01−4.3031E+00 A:   3.6741E−02   1.8256E−01   4.5416E−02 −8.0305E−02 B:−8.3929E−02 −2.6664E−01 −2.1488E−01   1.4138E−02 C: −1.0778E−01  1.3605E−01   2.1163E−01   7.1845E−03 D:   5.8965E−01 −5.3917E−03−1.0522E−01 −5.3835E−03 E: −4.6881E−01   1.0448E−02   2.5824E−02  1.1975E−03 F:   1.1719E−01 −7.0375E−03 −2.4802E−03 −9.1525E−05

The units of the radius of curvature, the thickness and the focal lengthin table 1 are expressed in mm, the surface numbers 0-13 represent thesurfaces sequentially arranged from the object-side to the image-sidealong the optical axis. In table 2, k represents the conic coefficientof the equation of the aspheric surface profiles, and A

B

C

D

E

F

G

H

. . . : represent the high-order aspheric coefficients. The tablespresented below for each embodiment are the corresponding schematicparameter, image plane curves and distortion curves, and the definitionsof the tables are the same as Table 1 and Table 2 of the firstembodiment. Therefore, an explanation in this regard will not beprovided again.

Referring to FIGS. 2A and 2B, FIG. 2A shows a four-piece infrared singlewavelength lens system in accordance with a second embodiment of thepresent invention, and FIG. 2B shows, in order from left to right, theimage plane curve and the distortion curve of the second embodiment ofthe present invention. A four-piece infrared single wavelength lenssystem in accordance with the second embodiment of the present inventioncomprises a stop 200 and a lens group. The lens group comprises, inorder from an object side to an image side: a first lens element 210, asecond lens element 220, a third lens element 230, a fourth lens element240, an IR cut filter 270, and an image plane 280, wherein thefour-piece infrared single wavelength lens system has a total of fourlens elements with refractive power. The stop 200 is disposed between animage-side surface 212 of the first lens element 210 and an object-sidesurface 221 of the second lens element 220.

The first lens element 210 with a positive refractive power has anobject-side surface 211 being convex near an optical axis 290 and theimage-side surface 212 being concave near the optical axis 290, theobject-side surface 211 and the image-side surface 212 are aspheric, andthe first lens element 210 is made of plastic material.

The second lens element 220 with a positive refractive power has theobject-side surface 221 being concave near the optical axis 290 and animage-side surface 222 being convex near the optical axis 290, theobject-side surface 221 and the image-side surface 222 are aspheric, andthe second lens element 220 is made of plastic material.

The third lens element 230 with a positive refractive power has anobject-side surface 231 being concave near the optical axis 290 and animage-side surface 232 being convex near the optical axis 290, theobject-side surface 231 and the image-side surface 232 are aspheric, andthe third lens element 230 is made of plastic material.

The fourth lens element 240 with a negative refractive power has anobject-side surface 241 being convex near the optical axis 290 and animage-side surface 242 being concave near the optical axis 290, theobject-side surface 241 and the image-side surface 242 are aspheric, thefourth lens element 240 is made of plastic material, and at least one ofthe object-side surface 241 and the image-side surface 242 is providedwith at least one inflection point.

The IR cut filter 270 made of glass is located between the fourth lenselement 240 and the image plane 280 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the second embodiment is shown in table 3,and the aspheric surface data is shown in table 4.

TABLE 3 Embodiment 2 f(focal length) = 2.51 mm, Fno = 1.96, FOV = 88.4deg. Focal surface Curvature Radius Thickness Material Index Abbe #length 0 object infinity 350 1 infinity 0 2 Lens 1 1.748 (ASP) 0.395plastic 1.636 24 4.87 3 3.853 (ASP) 0.075 4 stop infinity 0.416 0.425 5Lens 2 −13.624 (ASP) 0.414 plastic 1.636 24 23.24 6 −7.044 (ASP) 0.244 7Lens 3 −1.683 (ASP) 0.790 plastic 1.636 24 1.97 8 −0.829 (ASP) 0.032 9Lens 4 1.270 (ASP) 0.402 plastic 1.636 24 −3.08 10 0.668 (ASP) 0.671 11IR-filter infinity 0.300 glass 1.517 64.2 12 infinity 0.400 13 Imageinfinity infinity plane

TABLE 4 Aspheric Coefficients surface 2 3 5 6 K: −1.7067E+00 −3.4722E+01  3.1953E+02   2.0415E+01 A:   3.1501E−02   7.5638E−02 −2.2843E−01−1.4221E−01 B:   1.0523E−01 −3.3841E−01 −1.8532E−01 −5.4287E−02 C:−4.9762E−01   1.0715E+00 −1.2821E−01 −3.5515E−01 D:   1.2243E+00−2.4651E+00 −2.8022E−01   8.0429E−01 E: −1.6974E+00   1.0106E+00−2.7457E−02 −9.1044E−01 F   8.2512E−01   1.6373E+00 −1.5936E+00  3.8687E−01 surface 7 8 9 10 K:   6.4636E−01 −1.1237E+00 −7.7196E+00−3.5453E+00 A:   1.0126E−01   1.8602E−01   2.8056E−02 −9.1849E−02 B:−1.8320E−01 −2.9504E−01 −2.2412E−01   1.2143E−02 C: −9.4963E−02  1.5469E−01   2.1715E−01   1.0310E−02 D:   6.0474E−01 −7.1032E−03−1.0318E−01 −6.4022E−03 E: −4.6538E−01 −7.3579E−04   2.4084E−02  1.3330E−03 F   1.1184E−01 −2.4339E−03 −2.2056E−03 −9.8358E−05

In the second embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the second embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 3 and Table 4 asthe following values and satisfy the following conditions:

Embodiment 2 f[mm] 2.51 f2/f4 −7.54 Fno 1.96 f1/f23 2.61 FOV[deg.] 88.40f12/f34 1.04 f1/f2 0.21 f2/f34 5.72 f2/f3 11.79 f23/f4 −0.61 f3/f4 −0.64f1/f234 1.40 f1/f3 2.47 f123/f4 −0.64 f1/f4 −1.58 f/TL 0.61

Referring to FIGS. 3A and 3B, FIG. 3A shows a four-piece infrared singlewavelength lens system in accordance with a third embodiment of thepresent invention, and FIG. 3B shows, in order from left to right, theimage plane curve and the distortion curve of the third embodiment ofthe present invention. A four-piece infrared single wavelength lenssystem in accordance with the third embodiment of the present inventioncomprises a stop 300 and a lens group. The lens group comprises, inorder from an object side to an image side: a first lens element 310, asecond lens element 320, a third lens element 330, a fourth lens element340, an IR cut filter 370, and an image plane 380, wherein thefour-piece infrared single wavelength lens system has a total of fourlens elements with refractive power. The stop 300 is disposed between animage-side surface 312 of the first lens element 310 and an object-sidesurface 321 of the second lens element 320.

The first lens element 310 with a positive refractive power has anobject-side surface 311 being convex near an optical axis 390 and theimage-side surface 312 being concave near the optical axis 390, theobject-side surface 311 and the image-side surface 312 are aspheric, andthe first lens element 310 is made of plastic material.

The second lens element 320 with a positive refractive power has theobject-side surface 321 being concave near the optical axis 390 and animage-side surface 322 being convex near the optical axis 390, theobject-side surface 321 and the image-side surface 322 are aspheric, andthe second lens element 320 is made of plastic material.

The third lens element 330 with a positive refractive power has anobject-side surface 331 being concave near the optical axis 390 and animage-side surface 332 being convex near the optical axis 390, theobject-side surface 331 and the image-side surface 332 are aspheric, andthe third lens element 330 is made of plastic material.

The fourth lens element 340 with a negative refractive power has anobject-side surface 341 being convex near the optical axis 390 and animage-side surface 342 being concave near the optical axis 390, theobject-side surface 341 and the image-side surface 342 are aspheric, thefourth lens element 340 is made of plastic material, and at least one ofthe object-side surface 341 and the image-side surface 342 is providedwith at least one inflection point.

The IR cut filter 370 made of glass is located between the fourth lenselement 340 and the image plane 380 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the third embodiment is shown in table 5,and the aspheric surface data is shown in table 6.

TABLE 5 Embodiment 3 f(focal length) = 2.51 mm, Fno = 1.96, FOV = 95.4deg. Focal surface Curvature Radius Thickness Material Index Abbe #length 0 object infinity 350 1 infinity 0 2 Lens 1 1.763 (ASP) 0.401plastic 1.636 24 4.96 3 3.831 (ASP) 0.076 4 stop infinity 0.416 0.414 5Lens 2 −12.829 (ASP) 0.428 plastic 1.636 24 15.92 6 −5.613 (ASP) 0.264 7Lens 3 −1.548 (ASP) 0.738 plastic 1.636 24 1.97 8 −0.801 (ASP) 0.032 9Lens 4 1.483 (ASP) 0.443 plastic 1.636 24 −2.90 10 0.717 (ASP) 0.640 11IR-filter infinity 0.300 glass 1.517 64.2 12 infinity 0.400 13 Imageinfinity infinity plane

TABLE 6 Aspheric Coefficients surface 2 3 5 6 K: −1.9509E+00 −5.2504E+01−1.2544E+02 −4.8591E+00 A:   4.7657E−02   1.1408E−01 −2.3122E−01−1.7096E−01 B:   4.4791E−02 −4.1206E−01 −1.7162E−01   5.3600E−02 C:−3.1528E−01   1.3008E+00   5.7875E−02 −4.5947E−01 D:   9.2014E−01−3.2604E+00 −1.6347E+00   7.6499E−01 E: −1.3879E+00   2.8459E+00  3.1300E+00 −7.3590E−01 F   7.0026E−01   5.9787E−02 −3.8885E+00  2.8817E−01 surface 7 8 9 10 K:   4.3595E−01 −1.0344E+00 −1.3202E+01−4.2385E+00 A:   3.7854E−02   1.8177E−01   4.1167E−02 −8.0619E−02 B:−8.5938E−02 −2.6281E−01 −2.1205E−01   1.2802E−02 C: −1.0363E−01  1.3545E−01   2.1059E−01   8.2684E−03 D:   5.8870E−01 −5.1831E−03−1.0511E−01 −5.7591E−03 E: −4.7059E−01   1.0104E−02   2.5769E−02  1.2536E−03 F   1.1763E−01 −7.0154E−03 −2.4630E−03 −9.4439E−05

In the third embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the third embodiment, so an explanation inthis regard will not be provided again.

Moreover, these parameters can be calculated from Table 5 and Table 6 asthe following values and satisfy the following conditions:

Embodiment 3 f[mm] 2.51 f2/f4 −5.49 Fno 1.96 f1/f23 2.71 FOV[deg.] 95.40f12/f34 0.91 f1/f2 0.31 f2/f34 3.59 f2/f3 8.08 f23/f4 −0.63 f3/f4 −0.68f1/f234 1.42 f1/f3 2.52 f123/f4 −0.66 f1/f4 −1.71 f/TL 0.61

Referring to FIGS. 4A and 4B, FIG. 4A shows a four-piece infrared singlewavelength lens system in accordance with a fourth embodiment of thepresent invention, and FIG. 4B shows, in order from left to right, theimage plane curve and the distortion curve of the fourth embodiment ofthe present invention. A four-piece infrared single wavelength lenssystem in accordance with the fourth embodiment of the present inventioncomprises a stop 400 and a lens group. The lens group comprises, inorder from an object side to an image side: a first lens element 410, asecond lens element 420, a third lens element 430, a fourth lens element440, an IR cut filter 470, and an image plane 480, wherein thefour-piece infrared single wavelength lens system has a total of fourlens elements with refractive power. The stop 400 is disposed between animage-side surface 412 of the first lens element 410 and an object-sidesurface 421 of the second lens element 420.

The first lens element 410 with a positive refractive power has anobject-side surface 411 being convex near an optical axis 490 and theimage-side surface 412 being concave near the optical axis 490, theobject-side surface 411 and the image-side surface 412 are aspheric, andthe first lens element 410 is made of plastic material.

The second lens element 420 with a negative refractive power has theobject-side surface 421 being convex near the optical axis 490 and animage-side surface 422 being concave near the optical axis 490, theobject-side surface 421 and the image-side surface 422 are aspheric, andthe second lens element 420 is made of plastic material.

The third lens element 430 with a positive refractive power has anobject-side surface 431 being concave near the optical axis 490 and animage-side surface 432 being convex near the optical axis 490, theobject-side surface 431 and the image-side surface 432 are aspheric, andthe third lens element 430 is made of plastic material.

The fourth lens element 440 with a negative refractive power has anobject-side surface 441 being convex near the optical axis 490 and animage-side surface 442 being concave near the optical axis 490, theobject-side surface 441 and the image-side surface 442 are aspheric, thefourth lens element 440 is made of plastic material, and at least one ofthe object-side surface 441 and the image-side surface 442 is providedwith at least one inflection point.

The IR cut filter 470 made of glass is located between the fourth lenselement 440 and the image plane 480 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the fourth embodiment is shown in table 7,and the aspheric surface data is shown in table 8.

TABLE 7 Embodiment 4 f(focal length) = 2.55 mm, Fno = 1.87, FOV = 91.3deg. Focal surface Curvature Radius Thickness Material Index Abbe #length 0 object infinity 350 1 infinity 0 2 Lens 1 2.170 (ASP) 0.430plastic 1.636 24 4.34 3 10.914 (ASP) 0.056 4 stop infinity 0.416 0.489 5Lens 2 32.816 (ASP) 0.305 plastic 1.636 24 −13.99 6 6.774 (ASP) 0.262 7Lens 3 −2.234 (ASP) 0.691 plastic 1.636 24 1.66 8 −0.782 (ASP) 0.022 9Lens 4 1.203 (ASP) 0.375 plastic 1.636 24 −2.51 10 0.595 (ASP) 0.676 11IR-filter infinity 0.300 glass 1.517 64.2 12 infinity 0.400 13 Imageinfinity infinity plane

TABLE 8 Aspheric Coefficients surface 2 3 5 6 K: −1.5895E+01  1.3329E+02   8.9832E+02 −5.2962E+01 A:   1.2244E−01 −6.8686E−02−2.8479E−01 −1.0908E−01 B:   1.3920E−03 −1.7972E−01 −2.3450E−01−2.2483E−01 C: −7.8975E−01   2.5174E−01   3.9083E−02   3.3456E−01 D:  1.9307E+00   5.6603E−03   3.9625E−01 −5.3176E−01 E: −2.2538E+00−1.3463E+00 −1.5710E+00   2.7576E−01 F   9.7761E−01   1.5373E+00  9.2492E−01 −6.0225E−02 surface 7 8 9 10 K: −1.2578E+00 −3.7344E+00−1.2814E+00 −3.6924E+00 A:   3.1454E−01 −1.7236E−01 −3.4575E−01−1.2059E−01 B: −8.2832E−01   9.8428E−02   1.8045E−01   5.0285E−02 C:  1.5941E+00 −1.6756E−01 −6.1504E−02 −1.4408E−02 D: −1.8204E+00  2.8909E−01   1.2582E−02   1.9453E−03 E:   1.0330E+00 −1.7648E−01−1.3580E−03 −6.9597E−05 F −2.3056E−01   3.6051E−02   5.9110E−05−6.0275E−06

In the fourth embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the fourth embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 7 and Table 8 asthe following values and satisfy the following conditions:

Embodiment 4 f[mm] 2.55 f2/f4 5.58 Fno 1.87 f1/f23 2.44 FOV[deg.] 91.30f12/f34 1.72 f1/f2 −0.31 f2/f34 −4.27 f2/f3 −8.41 f23/f4 −0.71 f3/f4−0.66 f1/f234 1.03 f1/f3 2.61 f123/f4 −0.73 f1/f4 −1.73 f/TL 0.64

Referring to FIGS. 5A and 5B, FIG. 5A shows a four-piece infrared singlewavelength lens system in accordance with a fifth embodiment of thepresent invention, and FIG. 5B shows, in order from left to right, theimage plane curve and the distortion curve of the fifth embodiment ofthe present invention. A four-piece infrared single wavelength lenssystem in accordance with the fifth embodiment of the present inventioncomprises a stop 500 and a lens group. The lens group comprises, inorder from an object side to an image side: a first lens element 510, asecond lens element 520, a third lens element 530, a fourth lens element540, an IR cut filter 570, and an image plane 580, wherein thefour-piece infrared single wavelength lens system has a total of fourlens elements with refractive power. The stop 500 is disposed between animage-side surface 512 of the first lens element 510 and an object-sidesurface 521 of the second lens element 520.

The first lens element 510 with a positive refractive power has anobject-side surface 511 being convex near an optical axis 590 and theimage-side surface 512 being concave near the optical axis 590, theobject-side surface 511 and the image-side surface 512 are aspheric, andthe first lens element 510 is made of plastic material.

The second lens element 520 with a negative refractive power has theobject-side surface 521 being concave near the optical axis 590 and animage-side surface 522 being concave near the optical axis 590, theobject-side surface 521 and the image-side surface 522 are aspheric, andthe second lens element 520 is made of plastic material.

The third lens element 530 with a positive refractive power has anobject-side surface 531 being concave near the optical axis 590 and animage-side surface 532 being convex near the optical axis 590, theobject-side surface 531 and the image-side surface 532 are aspheric, andthe third lens element 530 is made of plastic material.

The fourth lens element 540 with a negative refractive power has anobject-side surface 541 being convex near the optical axis 590 and animage-side surface 542 being concave near the optical axis 590, theobject-side surface 541 and the image-side surface 542 are aspheric, thefourth lens element 540 is made of plastic material, and at least one ofthe object-side surface 541 and the image-side surface 542 is providedwith at least one inflection point.

The IR cut filter 570 made of glass is located between the fourth lenselement 540 and the image plane 580 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the fifth embodiment is shown in table 9,and the aspheric surface data is shown in table 10.

TABLE 9 Embodiment 5 f(focal length) = 2.54 mm, Fno = 1.96, FOV = 92.9deg. Focal surface Curvature Radius Thickness Material Index Abbe #length 0 object infinity 350 1 infinity 0 2 Lens 1 2.339 (ASP) 0.429plastic 1.636 24 4.28 3 20.778 (ASP) 0.000 4 stop infinity 0.416 0.525 5Lens 2 −16.328 (ASP) 0.354 plastic 1.636 24 −12.10 6 13.611 (ASP) 0.2527 Lens 3 −1.969 (ASP) 0.626 plastic 1.636 24 2.26 8 −0.910 (ASP) 0.022 9Lens 4 1.118 (ASP) 0.438 plastic 1.636 24 −4.65 10 0.683 (ASP) 0.694 11IR-filter infinity 0.300 glass 1.517 64.2 12 infinity 0.400 13 Imageinfinity infinity plane

TABLE 10 Aspheric Coefficients surface 2 3 5 6 K: −1.1246E+01  1.1099E+02   6.1845E+00   2.4935E+01 A:   5.9853E−02 −8.6413E−02−2.6998E−01 −1.0465E−01 B: −2.3996E−02 −9.9129E−02 −1.8062E−01−2.1756E−01 C: −5.8338E−01   7.3250E−02   1.5446E−02   3.4141E−01 D:  1.8193E+00 −8.4609E−02   3.1075E−01 −5.2346E−01 E: −2.7655E+00−5.3750E−01 −1.4404E+00   2.7999E−01 F   1.5352E+00   9.3605E−01  1.2956E+00 −3.7109E−02 surface 7 8 9 10 K: −3.5504E+00 −3.1970E+00−1.3252E+00 −3.3444E+00 A:   3.1257E−01 −1.5837E−01 −3.3444E−01−1.1831E−01 B: −8.6546E−01   1.0246E−01   1.8073E−01   5.0238E−02 C:  1.5932E+00 −1.7069E−01 −6.2110E−02 −1.3888E−02 D: −1.7950E+00  2.8826E−01   1.2504E−02   1.8671E−03 E:   1.0428E+00 −1.7547E−01−1.3530E−03 −9.4703E−05 F −2.4336E−01   3.5853E−02   6.2583E−05−1.9488E−06

In the fifth embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the fifth embodiment, so an explanation inthis regard will not be provided again.

Moreover, these parameters can be calculated from Table 9 and Table 10as the following values and satisfy the following conditions:

Embodiment 5 f[mm] 2.54 f2/f4 2.60 Fno 1.96 f1/f23 1.68 FOV[deg.] 92.90f12/f34 1.83 f1/f2 −0.35 f2/f34 −3.76 f2/f3 −5.35 f23/f4 −0.55 f3/f4−0.49 f1/f234 1.01 f1/f3 1.89 f123/f4 −0.48 f1/f4 −0.92 f/TL 0.63

In the present four-piece infrared single wavelength lens system, thelens elements can be made of plastic or glass. If the lens elements aremade of plastic, the cost will be effectively reduced. If the lenselements are made of glass, there is more freedom in distributing therefractive power of the four-piece infrared single wavelength lenssystem. Plastic lens elements can have aspheric surfaces, which allowmore design parameter freedom (than spherical surfaces), so as to reducethe aberration and the number of the lens elements, as well as the totaltrack length of the four-piece infrared single wavelength lens system.

In the present four-piece infrared single wavelength lens system, if theobject-side or the image-side surface of the lens elements withrefractive power is convex and the location of the convex surface is notdefined, the object-side or the image-side surface of the lens elementsnear the optical axis is convex. If the object-side or the image-sidesurface of the lens elements is concave and the location of the concavesurface is not defined, the object-side or the image-side surface of thelens elements near the optical axis is concave.

The four-piece infrared single wavelength lens system of the presentinvention can be used in focusing optical systems and can obtain betterimage quality. The four-piece infrared single wavelength lens system ofthe present invention can also be used in electronic imaging systems,such as, 3D image capturing, digital camera, mobile device, digital flatpanel or vehicle camera.

While we have shown and described various embodiments in accordance withthe present invention, it should be clear to those skilled in the artthat further embodiments may be made without departing from the scope ofthe present invention.

What is claimed is:
 1. A four-piece infrared single wavelength lenssystem, in order from an object side to an image side, comprising: afirst lens element with a positive refractive power, having anobject-side surface being convex near an optical axis and an image-sidesurface being concave near the optical axis, at least one of theobject-side surface and the image-side surface of the first lens elementbeing aspheric; a stop; a second lens element with a refractive power,at least one of an object-side surface and an image-side surface of thesecond lens element being aspheric; a third lens element with a positiverefractive power, having an object-side surface being concave near theoptical axis and an image-side surface being convex near the opticalaxis, at least one of the object-side surface and the image-side surfaceof the third lens element being aspheric; and a fourth lens element witha negative refractive power, having an object-side surface being convexnear the optical axis and an image-side surface being concave near theoptical axis, at least one of the object-side surface and the image-sidesurface of the fourth lens element being aspheric; wherein a focallength of the first lens element is f1, a focal length of the third lenselement is f3, and they satisfy the relation: 1.4<f1/f3<3.0; arefractive index of the fourth lens element is N4, an Abbe number of thefourth lens element is V4, and they satisfy the relations: 1.61<N4;V4<25.
 2. The four-piece infrared single wavelength lens system asclaimed in claim 1, wherein the focal length of the first lens elementis f1, a focal length of the second lens element is f2, and they satisfythe relation: −1.0<f1/f2<1.0.
 3. The four-piece infrared singlewavelength lens system as claimed in claim 1, wherein a focal length ofthe second lens element is f2, the focal length of the third lenselement is f3, and they satisfy the relation: −10.4<f2/f3<13.8.
 4. Thefour-piece infrared single wavelength lens system as claimed in claim 1,wherein the focal length of the third lens element is f3, a focal lengthof the fourth lens element is f4, and they satisfy the relation:−1.0<f3/f4<−0.1.
 5. The four-piece infrared single wavelength lenssystem as claimed in claim 1, wherein the focal length of the first lenselement is f1, a focal length of the fourth lens element is f4, and theysatisfy the relation: −2.1<f1/f4<−0.5.
 6. The four-piece infrared singlewavelength lens system as claimed in claim 1, wherein a focal length ofthe second lens element is f2, a focal length of the fourth lens elementis f4, and they satisfy the relation: −9.0<f2/f4<7.1.
 7. The four-pieceinfrared single wavelength lens system as claimed in claim 1, whereinthe focal length of the first lens element is f1, a focal length of thesecond lens element and the third lens element combined is f23, and theysatisfy the relation: 1.2<f1/f23<3.1.
 8. The four-piece infrared singlewavelength lens system as claimed in claim 1, wherein a focal length ofthe first lens element and the second lens element combined is f12, afocal length of the third lens element and the fourth lens elementcombined is f34, and they satisfy the relation: 0.48<f12/f34<2.23. 9.The four-piece infrared single wavelength lens system as claimed inclaim 1, wherein a focal length of the second lens element is f2, afocal length of the third lens element and the fourth lens elementcombined is f34, and they satisfy the relation: −5.3<f2/f34<6.7.
 10. Thefour-piece infrared single wavelength lens system as claimed in claim 1,wherein a focal length of the second lens element and the third lenselement combined is f23, a focal length of the fourth lens element isf4, and they satisfy the relation: −1.0<f23/f4<−0.2.
 11. The four-pieceinfrared single wavelength lens system as claimed in claim 1, whereinthe focal length of the first lens element is f1, a focal length of thesecond lens element, the third lens element and the fourth lens elementcombined is f234, and they satisfy the relation: 0.7<f1/f234<1.8. 12.The four-piece infrared single wavelength lens system as claimed inclaim 1, wherein a focal length of the first lens element, the secondlens element and the third lens element combined is f123, a focal lengthof the fourth lens element is f4, and they satisfy the relation:−1.0<f123/f4<−0.15.
 13. The four-piece infrared single wavelength lenssystem as claimed in claim 1, wherein a focal length of the four-pieceinfrared single wavelength lens system is f, a distance from theobject-side surface of the first lens element to an image plane alongthe optical axis is TL, and they satisfy the relation: 0.4<f/TL<0.85.